Typically, the stator vanes of the gas turbine stator assembly for use in the gas turbine engine each comprise an air-cooling mechanism for increasing a heat resistance of its blades exposed to high-temperature combustion gas generated by the combustors. The mechanism comprises a cooling cavity or passage defined within each blade into which a compressed air from the compressor is introduced for the cooling of the blade. According to this mechanism, an increase of the cooling air consumed for the blade cooling results in a decrease in efficiency of the gas turbine engine. This needs the blade to be effectively cooled with a minimum amount of air. Typically, however, the stator vane is manufactured by molding and therefore it is relatively difficult to form small inlets for introducing small amount of cooling air into the passage of the blade. To solve this problem, JP 2003-286805 (A) discloses another cooling mechanism in which a flow-rate control plate with a number of small apertures is used as a member to be inserted in the air passage within the stator vane in order to effectively cool the stator vane with a limited amount of air. This mechanism needs the insert member and therefore results in a structural complexity and a cost increase.
An alternative may be, as shown in FIG. 5, to place a plate 54 with a small aperture 58 defined therein so that it covers the inlet 53 of the cooling passage 52 defined within each blade 51 of the stator assembly 50 to restrict the amount of air to be supplied into the passage. This arrangement may ensure that only a limited amount of air A be introduced into the cooling passage 52 through the aperture 58 and the inlet 53. Disadvantageously, a numerical analysis conducted by the inventors revealed that the flow of air A entering through the inlet 53 advanced obliquely to cause air stagnation zones S1 and S2 in the front and rear sides of the flow, adjacent the inlet 53. In particular, the front stagnation zone was formed immediately behind the front the wall portions where the high-temperature combustion gas G would hit directly and therefore deemed to be the most needed for cooling, which failed the blade 51 to be cooled effectively.